Herbicidal compounds

ABSTRACT

A compound of the general formula (I) ##STR1## wherein A represents a group of general formula ##STR2## and R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , X, Q 2 , Q 3 , and n are as described in the specification. The compounds of formula (I) are useful as agricultural herbicides.

This is a 35 U.S.C. §371 application of PCT/EP94/01759 filed May 26,1994.

The present invention relates to herbicidal compounds, and in particularto herbicidal carboxamide derivatives, their preparation and their use.

European Patent Specification No. 0 488 474 A1 describes and claimsphenoxypicolinamides of the general formula ##STR3## wherein n is aninteger from 1 to 5 and the or each X independently represents ahydrogen or halogen atom, an alkyl or alkoxy group optionallysubstituted by one or more of the same or different substituentsselected from halogen atoms and cyano, hydroxy and alkoxy groups, or acyano, nitro, alkenyloxy, alkynyloxy, alkylthio, haloalkylthio,alkenylthio or alkynylthio group;

m is 0 or an integer from 1 to 3 and the or each Y independentlyrepresents a halogen atom or an alkyl or haloalkyl group;

Z represents an oxygen atom or a sulphur atom; and

R¹ and R² each, independently, represents a hydrogen atom, an alkylgroup optionally substituted by one or more of the same or differentsubstituents selected from halogen atoms or hydroxy, cyano, alkoxy,alkylthio, alkoxycarbonyl, or mono- or di-alkylamino groups, an alkenyl,alkynyl, cycloalkyl, or optionally substituted cycloalkylalkyl group, ora hydroxy, alkoxy, alkenyloxy, alkynyloxy, alkoxycarbonyl, amino, mono-or di-alkylamino, alkoxycarbonylamino group, an arylamino groupoptionally substituted by a halogen atom, or a dialkylcarbamoyl group;or

R¹ and R² together represent an alkylene chain which is optionallyinterrupted by an oxygen or sulphur atom or by a group --NR-- in which Rrepresents a hydrogen atom or an alkyl group.

These compounds are shown to have herbicidal properties.

Variation of the central ring of such compounds and of relatedpyridyloxy- and pyrazolyloxy- derivatives, to include additional heteroatoms have now been found to show high herbicidal activity. Usefulintermediates to such new compounds have also been found to exhibitherbicidal properties.

The present invention accordingly provides a compound of the generalformula ##STR4## wherein A represents a group of the general formula##STR5## in which the or each X independently represents a halogen atomor an optionally substituted alkyl, alkoxy, aryl or aryloxy group, or analkenyloxy, alkynyloxy, alkylthio, haloalkylthio, alkenylthio,alkenylthio, alkylsulphinyl, alkylsulphonyl or cyano group; and n is 0,an integer from 1 to 4, or, for the phenyl group, 5; or A represents agroup of the general formula ##STR6## in which each of R⁴ , R⁵ and R⁶independently represents a hydrogen or halogen atom, an optionallysubstituted alkyl, alkenyl, alkynyl, cycloalkyl, cycloalkylalkyl, aryl,aralkyl, alkaryl, alkoxy, amino, mono- or di-alkylamino,alkoxycarbonylamino, arylamino, dialkylcarbamoyl, acyl or acylamidogroup or a cyano group, with the proviso that R⁵ and R⁶ do not representan acyl, acylamido or cyano group;

Z represents an oxygen or sulphur atom;

R¹ and R² each independently represents a hydrogen atom or an optionallysubstituted alkyl, alkenyl, alkynyl, cycloalkyl, cycloalkylalkyl,heterocyclyl, aryl, aralkyl, alkaryl, hydroxy, alkoxy, alkenyloxy,alkynyloxy, alkylcarbonyl, alkoxycarbonyl, amino, mono- ordi-alkylamino, alkoxycarbonylamino, arylamino, arylalkylamino ordialkylcarbamoyl group, or together represent an alkylene chain which isoptionally interrupted by an oxygen or sulphur atom or by a group --N⁷-- in which R⁷ represents a hydrogen atom or an alkyl group; and

Q¹, Q² and Q³ each represents a nitrogen atom or a group CR³ in which R³represents a hydrogen atom or an optionally substituted alkyl, alkoxy,alkylthio or mono- or di-alkylamino group, provided that all three ofQ¹, Q² and Q³ are not a nitrogen atom or the group CR³.

Generally, herein, any alkyl, alkenyl or alkynyl moiety which is orforms part of a group represented by X, R¹, R², R³, R⁴, R⁵, R⁶ or R⁷suitably contains up to 12 carbon atoms, conveniently up to 8,preferably up to 6, and especially up to 4, carbon atoms. Such moietiesmay be linear or branched chain moieties. As part of a larger group,alkyl moieties are especially methyl or ethyl.

A cycloalkyl moiety suitably contains from 3 to 10, preferably from 3 to8, carbon atoms. An aryl group is usefully a single ring or fused ringsystem having from 6 to 14 ring members, preferably 6 or 10 ring atoms;a preferred aryl group is phenyl.

A heterocyclic group is suitably a single ring system having 3 to 6 ringmembers selected from carbon atoms and at least one nitrogen, oxygen orsulphur atom; preferred heterocyclic groups are morpholino and thienyl.

Halogen is used to denote fluorine, chlorine, bromine or iodine,especially chlorine or fluorine. A preferred haloalkyl moiety istrifluoromethyl.

An acyl group is the group formed by the removal of hydroxyl from acarboxyl group, and is used herein to include formyl and optionallysubstituted alkylcarbonyl and arylcarbonyl groups.

An alkylene chain suitably has from 3 to 6, preferably 4 or 5 chainmembers.

Optional substituents may be any of those customarily employed in thedevelopment of biocidal compounds, and/or the modification of suchcompounds to influence their activity, persistence, penetration or anyother property. Specific examples of such substituents include halogen,especially fluorine, chlorine or bromine atoms, and phenyl, nitro,cyano, amino, hydroxy, alkyl, alkoxy, mono- or di-alkylamino groups,haloalkyl, haloalkoxy, formyl, alkoxycarbonyl, carboxy, halophenylgroups and heterocyclyl, especially thienyl, groups. Alkyl moieties ofsuch optional substituents usefully have from 1 to 6 carbon atoms,preferably 1 or 2 carbon atoms.

Where group A represents a phenyl or pyridyl ring, the substituent(s) X,if present, may be at any of the free positions on the ring. Preferablya substituent X is present meta to the bond to the oxygen atom offormula I. Especially useful examples of the substituent(s) X includehalogen atoms and haloalkyl groups. Preferably X represents a chlorineatom or a trifluorimethyl group. There are usefully either no Xsubstituents or, preferably, only 1 X substituent.

Where A represents a pyrazolyl group, preferably R⁶ represents ahydrogen atom, and each of R⁴ and R⁵ independently represents an alkyl,cycloalkyl, haloalkyl or an aryl group, more preferably a C₁₋₄ alkyl, orhalo(C₁₋₂) alkyl group, especially a methyl or trifluoroalkyl group.Preferably, R⁴ represents a methyl group and R⁵ represents a methyl ortrifluoromethyl group.

It is especially preferred that A represents a 3-trifluoromethylphenylgroup.

Z preferably represents an oxygen atom.

The substituents R¹ and R² may be the same or different. Preferably eachof R¹ and R² represents a hydrogen atom, a C₁₋₆ alkyl group, a C₃₋₆cycloalkyl group or a phenyl group which is unsubstituted orhalo-substituted. Examples of such preferred meanings include one of R¹and R² representing a hydrogen atom or a C₁₋₄ alkyl group, eg ethyl,whilst the other represent a hydrogen atom, a C₁₋₆ alkyl group, egethyl, whilst the other represents a hydrogen atom, a C₁₋₆ alkyl group,eg butyl, a cyclopropyl group, a phenyl group or a fluorophenyl group,eg 4-fluorophenyl or 2,4-difluorophenyl.

Especially preferred are compounds in which one of R¹ and R² is hydrogenor ethyl and the other is 4-fluorophenyl.

The central ring of the compounds of formula I is a heteroaryl ring inwhich at least 2 of the ring members are nitrogen atoms. Examples ofsuch rings include pyrimidine, pyrazine and triazine rings.

Preferably, one of Q¹, Q² and Q³ represents a nitrogen atom, a secondrepresents the group CR³ in which R³ represents a hydrogen atom, a C₁₋₄alkyl group or a di(C₁₋₄)alkylamino, eg dimethylamino, group, and thethird represents the group ═CH--. Thus preferably the central ring is anoptionally substituted pyrimidine or pyrazine ring. Especially preferredare compounds in which the central ring is an unsubstituted pyrimidineor pyrazine ring or a 6-methyl- pyrimidinyl group.

The present invention further provides a process for the preparation ofa compound of general formula I, which comprises reacting a compound ofthe general formula II ##STR7## in which A, Z, Q¹, Q² and Q³ are asdefined above, or an activated derivative thereof, with a compound ofthe general formula III

    HNR.sup.1 R.sup.2                                          (III)

in which R¹ and R² are as defined above, or, for a compound of theinvention in which Q¹ and Q³ are both nitrogen and Q² is the group═CH--, cyclising a compound of the general formula IV ##STR8## in whichA, R¹ and R² are as defined above, and L represents a leaving group, byreaction with an isothiourea, and converting the resultingthio-substituted compound into a compound of the invention by removal orreplacement of the thio substituent.

A leaving group is any group that will, under the reaction conditions,cleave from the starting material, thus enabling substitution at thatspecific site. The leaving group L may suitably be a halogen atom, forexample a bromine atom or, especially a chlorine atom, an alkoxy group,suitably C₁₋₄ alkoxy, especially methoxy, an alkyl- or aryl-sulphoniumgroup, especially a C₁₋₆ alkyl-, phenyl- or tolyl-sulphonium group, oran alkyl- or aryl-sulphonic acid group, especially a C₁₋₆ alkyl-,phenyl- or tolyl-sulphonic acid group.

Activated derivatives of the compounds or the general formula II arecompounds in which the hydroxy group of the acid function has beenreplaced by a suitable leaving group, for instance a halogen atom, forexample a bromine atom, or especially, a chlorine atom, an alkoxy group,suitably C₁₋₄ alkoxy, especially methoxy, or an imidazole group.Preparation of an activated derivative may be effected by conventionalmeans, for example the acid chloride may be prepared using thionylchloride.

The process of the invention is suitably carried out in the presence ofan inert organic solvent, for example dimethylformamide ordimethylsulphoxide, or an aromatic hydrocarbon, for example benzene ortoluene, or a halogenated hydrocarbon, for example dichloromethane, oran ether, for example diethyl ether, or an ester, for example ethylacetate. The process is suitably carried out at a temperature in therange of from 0° to 100° C., preferably at the reflux temperature of thereaction mixture, and suitably in the presence of a base, for examplepotassium hydroxide, and a copper catalyst, such as cuprous chloride.

Suitably the reaction is carried out using substantially equimolaramounts of the reactants. However, it can be expedient to use onereactant in excess.

When the compounds of formula I are prepared from an acid halidederivative of the compound of formula II, the reaction is convenientlycarried out at a temperature in the range of from 0° to 50° C.,preferably at ambient temperature, and suitably in the presence of abase, for example potassium carbonate or, preferably, an amine base,such as triethylamine.

Other activated derivatives may require different reaction conditionswhich will be within the knowledge of the skilled person in the art, oreasily ascertainable by such by routine experimentation. For an esterderivative (where the hydroxy function has been replaced by an alkoxygroup), the reaction is suitably carried out at a temperature in therange of from 0° to 100° C., preferably at ambient temperature, and inthe absence of an added base.

Compounds of formula I in which Z represents a sulphur atom may beprepared from a compound of formula I in which Z represents an oxygenatom by reaction with phosphorous pentasulphide under standardconditions, for example by heating, suitably under reflux, in thepresence of an inert aromatic solvent, for example benzene, toluene,pyridine or quinoline.

The compounds of the present invention may be isolated and purified byconventional techniques, for example by solvent extraction, evaporationfollowed by recrystallisation, or by chromatography on silica oralumina.

The compounds of formula II may be prepared by hydrolysis of cyanoderivatives of the general formula V ##STR9## in which A, Q¹, Q² and Q³have the meanings given above.

This reaction is suitably carried out in the presence of a solvent whichis inert with respect to the reaction components, for example water, orethylene glycol, using as hydrolysis reactants acids such ashydrochloric acid, sulphuric acid, or, for the pyridyloxy compounds offormula V, phosphoric acid, or bases such as potassium hydroxide orsodium hydroxide, at a temperature in the range of from 0° to 150° C.,for example at reflux. It is not essential for an inert solvent to beused; the reaction may still proceed if the cyano compound V issuspended in the hydrolysis reactant.

It is possible via this reaction to prepare compounds of formula I inwhich each of R¹ and R² represents a hydrogen atom, in addition to theacid intermediate. Isolation of the carbamide is possible via solventextraction and chromatography on silica gel. Compounds of formula V maysuitably be prepared by reacting a compound of the general formula VI##STR10## in which Q¹, Q² and Q³ are as hereinbefore defined, and Y is aleaving group as defined above, preferably a halogen atom, especiallychlorine, with a compound of formula VII

    A--OH

or an alkali metal salt thereof. Suitable reaction conditions are thesame as those specified above for the reaction of compounds of formulaeII and III.

Compounds of formula VI may be prepared by conventional or literaturemethods, such as the procedure of Daves et al., J. Het. Chem. 1 (1964),130.

It is also possible to prepare the cyano compounds of formula V byconversion of an appropriate precursor group of corresponding compounds,e.g. compounds corresponding to those of the formula V but with, forexample, a methylsulphonyl group or a dimethylamino group in place ofthe cyano group. The conversion of such precursor groups is usuallyeffected by reaction with a suitable cyanide compound, such as sodium orpotassium cyanide or tertiaryalkylammonium cyanide, e.g. tertiary ethyl-or tertiary butyl-ammonium cyanide. The precursor compounds maythemselves be prepared analogously to compounds of formula V by reactionof a suitably substituted heterocyclic compound (corresponding to acompound of formula VI) with a compound of formula VII or alkali metalsalt thereof. Alternatively the precursor compounds may be derived froma compound of formula ##STR11## where A, Q¹, Q² and Q³ are as previouslydefined and Hal is a suitable halogen leaving group, e.g. chlorine; suchcompounds themselves may be prepared from the constituent ring compoundsanalogously to the reaction of compounds VI and VII above.

The compounds of formula II may also be prepared by reacting a compoundof the general formula VIII ##STR12## in which Z, Q¹, Q² and Q³ are asspecified above, L represents a leaving group, preferably a halogenatom, for example chlorine, and AIK represents an alkyl group, forexample an ethyl group, with a compound of the general formula VII, oran alkali metal salt thereof, especially a sodium salt thereof,utilising the same reaction conditions as for the reaction of compoundsof formulae II and III.

The compounds of formulae II, and alkyl esters thereof, and V formfurther aspects of the present invention.

The compounds of formula VIII may be prepared by reaction of a compoundof formula VII, or alkali metal salt thereof, with an appropriateheterocyclic compound by the general reaction conditions specified abovefor such reactions, utilising the necessary procedures for incorporationinto the heterocyclic compound of a suitable leaving group as areavailable to the person skilled in the art.

The compounds of formula VII are either known or preparable byconventional or literature methods, for example by the methods of J.Het. Chem. 28 (1991), 1971 ff, and j. Het. Chem. 27 (1990), 243 ff.

For certain heterocyclic variants of the formula I, it may be necessaryto use cyclisation synthesis procedures. Thus for 1,3,5-triazinecompounds of formula I, i.e. in which Q¹ and Q³ are both nitrogen and Q²is a group ═CH--, it is appropriate to use a preparation process whichcomprises cyclising a compound of the general formula IV ##STR13## inwhich A, R¹ and R² are as hereinbefore defined, and L represents aleaving group, preferably a halogen atom, for example chlorine, byreaction with an isothiourea, for example isothiourea itself or anS-alkyl, preferably S-methyl, isothiourea, and converting the resultingthio-substituted compound into a compound of formula I by removal orreplacement of the thio substituent.

The reaction is conveniently carried out at room temperature using asuitable tertiaryalkyl amine base, eg triethylamine, and inert solvent,eg dioxane.

Compounds of formula IV maybe prepared by the condensation of compoundsof the general formula A-OCN, in which A is as hereinbefore defined,with an appropriate oxalic half anilide half halide at elevatedtemperature, for example a temperature in the range of from 30° C. to60° C., and in the presence of an inert solvent, eg dioxane. The cyanatecompounds may be prepared by conventional procedures from a compounds offormula VII by reaction with a cyanogen halide, for example cyanogenbromide.

Compounds of formula I and alkyl esters of compounds of formula II andcompounds of formula V have been found to have useful herbicidalactivity. Accordingly, the present invention further provides aherbicidal composition which comprises a compound of formula I or acompound of formula II or an alkyl ester thereof or a compound offormula V in association with a carrier, and a method of making such acomposition which comprises bringing a compound of formula I intoassociation with a carrier.

The invention further provides the use of a compound of formula I or ofa compound of formula II or an alkyl ester thereof or a compound offormula V or of a composition of the invention, as a herbicide. Alsoprovided is a method of combating undesired plant growth at a locus bytreating the locus with a compound of formula I, with a compound offormula II or an alkyl ester thereof or compound of formula V or acomposition of the invention. The locus may be, for example, the soil orplants in a crop area. The dosage of active ingredient used may, forexample, be in the range of from 0.01 to 10 kg/ha.

A carrier in a composition according to the invention is any materialwith which the active ingredient is formulated to facilitate applicationto the locus to be treated, which may for example be a plant, seed orsoil, or to facilitate storage, transport or handling. A carrier may bea solid or a liquid, including a material which is normally gaseous butwhich has been compressed to form a liquid, and any of the carriersnormally used in formulating herbicidal compositions may be used.Preferably compositions according to the invention contain 0.5 to 95% byweight of active ingredient.

Suitable solid carriers include natural and synthetic clays andsilicates, for example natural silicas such as diatomaceous earths;magnesium silicates, for example talcs; magnesium aluminium silicates,for example attapulgites and vermiculites; aluminium silicates, forexample kaolinites, montmorillonites and micas; calcium carbonate;calcium sulphate; ammonium sulphate; synthetic hydrated silicon oxidesand synthetic calcium or aluminium silicates; elements, for examplecarbon and sulphur; natural and synthetic resins, for example coumaroneresins, polyvinyl chloride, and styrene polymers and copolymers; solidpolychlorophenols; bitumen; waxes; and solid fertilisers, for examplesuperphosphates.

Suitable liquid carriers include water; alcohols, for exampleisopropanol and glycols; ketones, for example acetone, methyl ethylketone, methyl isobutyl ketone and cyclohexanone;

ethers; aromatic or araliphatic hydrocarbons, for example benzene,toluene and xylene; petroleum fractions, for example kerosine and lightmineral oils; chlorinated hydrocarbons, for example carbontetrachloride, perchloroethylene and trichloroethane. Mixtures ofdifferent liquids are often suitable.

Agricultural compositions are often formulated and transported in aconcentrated form which is subsequently diluted by the user beforeapplication. The presence of small amounts of a carrier which is asurface-active agent facilitates this process of dilution. Thuspreferably at least one carrier in a composition according to theinvention is a surface-active agent. For example the composition maycontain at least two carriers, at least one of which is a surface-activeagent.

A surface-active agent may be an emulsifying agent, a dispersing agentor a wetting agent; it may be nonionic or ionic.

Examples of suitable surface-active agents include the sodium or calciumsalts of polyacrylic acids and lignin sulphonic acids; the condensationproducts of fatty acids or aliphatic amines or amides containing atleast 12 carbon atoms in the molecule with ethylene oxide and/orpropylene oxide; fatty acid esters of glycerol, sorbitol, sucrose orpentaerythritol; condensates of these with ethylene oxide and/orpropylene oxide; condensation products of fatty alcohol or alkylphenols, for example p-octylphenol or p-octylcresol, with ethylene oxideand/or propylene oxide; sulphates or sulphonates of these condensationproducts; alkali or alkaline earth metal salts, preferably sodium salts,of sulphuric or sulphonic acid esters containing at least 10 carbonatoms in the molecule, for example sodium lauryl sulphate, sodiumsecondary alkyl sulphates, sodium salts of sulphonated castor oil, andsodium alkylaryl sulphonates such as dodecylbenzene sulphonate;

and polymers of ethylene oxide and copolymers of ethylene oxide andpropylene oxide.

The compositions of the invention may for example be formulated aswettable powders, dusts, granules, solutions, emulsifiable concentrates,emulsions, suspension concentrates and aerosols. Wettable powdersusually contain 25, 50 or 75% w of active ingredient and usually containin addition to solid inert carrier, 3-10% w of a dispersing agent and,where necessary, 0-10% w of stabiliser(s) and/or other additives such aspenetrants or stickers. Dusts are usually formulated as a dustconcentrate having a similar composition to that of a wettable powderbut without a dispersant, and are diluted in the field with furthersolid carrier to give a composition usually containing 1/2-0% w ofactive ingredient. Granules are usually prepared to have a size between10 and 100 BS mesh (1.676-0.152 mm), and may be manufactured byagglomeration or impregnation techniques. Generally, granules willcontain 1/2-75% w active ingredient and 0-10% w of additives such asstabilisers, surfactants, slow release modifiers and binding agents. Theso-called "dry flowable powders" consist of relatively small granuleshaving a relatively high concentration of active ingredient.Emulsifiable concentrates usually contain, in addition to a solvent and,when necessary, co-solvent, 10-50% w/v active ingredient, 2-20% w/vemulsifiers and 0-20% w/v of other additives such as stabilisers,penetrants and corrosion inhibitors. Suspension concentrates are usuallycompounded so as to obtain a stable, non-sedimenting flowable productand usually contain 10-75% w active ingredient, 0.5-15% w of dispersingagents, 0.1-10% w of suspending agents such as protective colloids andthixotropic agents, 0-10% w of other additives such as defoamers,corrosion inhibitors, stabilisers, penetrants and stickers, and water oran organic liquid in which the active ingredient is substantiallyinsoluble; certain organic solids or inorganic salts may be presentdissolved in the formulation to assist in preventing sedimentation or asanti-freeze agents for water.

Aqueous dispersions and emulsions, for example compositions obtained bydiluting a wettable powder or a concentrate according to the inventionwith water, also lie within the scope of the invention. The saidemulsions may be of the water-in-oil or of the oil-in-water type, andmay have a thick `mayonnaise`-like consistency.

The composition of the invention may also contain-other ingredients, forexample compounds possessing insecticidal or fungicidal properties orother herbicides.

The following examples illustrate the invention. All structures wereconfirmed by mass spectroscopy and/or 300'H nmr.

EXAMPLES 1 to 8 EXAMPLE 1 Preparation of2-(3-trifluoromethylphenoxy)pyrimidine-4-carbamide and of2-(3-trifluoromethylphenoxy)-pyrimidine-4-(N-(4-fluorophenyl))carboxamide

Compound 1--2-(3-Trifluoromethylphenoxy)pyrimidine-4-carbonitrile

The starting material, 2-chloropyrimidine-4-carbonitrile, was preparedaccording to the procedure of Daves et al. (J. Het. Chem. 1, (1964),130).

1.6 g 3-trifluoromethylphenol was dissolved in 50 ml of toluene and 1.8g of Na-methylate solution (30% in methanol) was added and stirred.After 10 minutes the solution was evaporated to dryness. A solution of1.4 g 2-chloropyrimidine-4-carbonitrile in 15 ml dimethylformamide wasadded and the mixture stirred for 10 minutes and evaporated to dryness.The residue was dissolved in 50 ml ethyl acetate and washed with 50 mlwater. The organic layer was dried with Na₂ SO₄ and evaporated. Theresidue was purified on silica gel with toluene/ethyl acetate as eluantto give 2.3 g (86.8%) of pure 2-(3-trifluoromethylphenoxy)pyrimidine-4-carbonitrile.

NMR (CDCl₃):7.3-7.5(m,4H,Arom.);7.55(d,1H,Arom.); 8.7(d,1H,Arom.)

Compound 2--2-(3-trifluoromethylphenoxy)pyrimidine-4-carbamide and

Compound 3--2-(3-trifluoromethylphenoxy)pyrimidine-4-carboxylic acid

7.8 g of 2-(3-trifluoromethylphenoxy)pyrimidine-4-carbonitrile (preparedas above) and 17 ml conc. HCl were stirred for 45 minutes at 65° C.,cooled to room temperature and diluted with 80 ml water. The residue wascollected, dissolved in 50 ml ethyl acetate and extracted twice with 50ml 0.1N NaOH. The water layer was acidified with conc. HCl and the2-(3-trifluoromethylphenoxy)-pyrimidine-4-carboxylic acid collected anddried to give 1.4 g (17.4%) of white crystals with m.p. 180°-183° C.(with decomposition). The organic layer was evaporated and the residuewas purified on silica gel with toluene/ethylacetate as eluent to give3.7 g (44.4%) 2-(3-trifluoromethylphenoxy)-pyrimidine-4-carbamide aswhite crystals of m.p. 113° C.

Compound4--2-(3-trifluoromethylphenoxy)pyrimidine-4-(N-(4-fluorophenyl))-carboxamide

1.0 g of 2-(3-trifluoromethylphenoxy)pyrimidine-4-carboxylic acid(prepared as above) was dissolved in 5 ml SOCl₂, drop ofdimethylformamide was added and the mixture stirred at refluxtemperature for 30 minutes, excess SOCl₂ distilled off, 10 ml of tolueneadded and evaporated. The residue was dissolved in 15 ml of toluene andadded over 3 minutes to a solution of 0.4 g 4-fluoroaniline and 0.4 g oftriethylamine in 20 ml toluene and stirred for 5 minutes at roomtemperature. The mixture was poured into 30 ml of water, the organiclayer was washed with 20 ml dil. HCl, 20 ml water, 20 ml dil. Na₂ CO₃-solution and finally with 20 ml of water, dried over Na₂ SO₄ andevaporated to give 1.27 g (96%) of white crystals of Compound 4, of m.p.(83°-92° C.).

EXAMPLES 2

Table 1 contains compounds nos. 5 to 9 synthesised according to theprocedure of Example 1.

                  TABLE 1                                                         ______________________________________                                         ##STR14##                                                                    Compound                                                                      No.     R.sub.1  R.sub.2      m.p. (°C.)                                                                    yield (%)                                ______________________________________                                        5       H        C.sub.6 H.sub.5                                                                            60-61  37.9                                     6       C.sub.2 H.sub.5                                                                        C.sub.6 H.sub.5                                                                            81-87  51.3                                     7       H        CH.sub.2 CH(CH.sub.3).sub.2                                                                oil    34.2                                     8       H        2,4-di-FC.sub.6 H.sub.3                                                                    79     41.5                                     9       H        cyclopropyl  oil    38.7                                     ______________________________________                                    

EXAMPLE 3 Preparation of4-(3-trifluoromethylphenoxy)pyrimidine-2-carbamide and4-(3-trifluoromethylphenoxy)pyrimidine-2-(N-(4-fluorophenyl))carboxamide

Compound 10--2-Chloro-4-(3-trifluoromethylphenoxy)pyrimidine

16.21 g of 3-trifluoromethylphenol was dissolved in 18 g 30% sodiummethylate solution, stirred for 10 minutes and evaporated to dryness,the residue dissolved in toluene and again evaporated to dryness. Asolution of 14.9 g 2,4-dichloropyrimidine in 50 ml dimethylformamide wasadded at room temperature and the mixture stirred for 15 minutes. Thesolution was reduced to 5 ml, poured into 50 ml water and extractedtwice with 50 ml ethyl acetate. The combined organic layers were driedover Na₂ SO₄, evaporated and the residue was purified on silica gel withtoluene/ethyl acetate to give 18.3 g (66.6%) of white crystals ofCompound 10 of m.p. 48°-53° C.

Compound 11--2-Cyano-4-(3-trifluoromethylphenoxy)pyrimidine To asolution of 0.66 g trimethylamine in 20 g dimethylformamide were added2.8 g of 2-chloro-4-(3-trifluoromethylphenoxy)pyrimidine (prepared asabove) at 0° C. at 0° C. The solution was allowed to warm to roomtemperature with stirring for 3.5 hours. 1.6 g tetraethylammoniumcyanide were added in one portion and the mixture stirred for another 30minutes. The solution was then diluted with 100 ml of water andextracted three times with 50 ml ethyl acetate. The combined organiclayers were dried over Na₂ SO₄, evaporated and the residue was purifiedon silica gel with toluene/ethyl acetate to give 2.2 g (83%) of paleyellow crystals of Compound 11, m.p. 56° C.

Compound 12--4-(3-trifluoromethylphenoxy)pyrimidine-2-carbamide

Compound 13--4-(3-trifluoromethylphenoxy)pyrimidine-2-carboxylic acid

5.3 g of 2-cyano-4-(3-trifluoromethylphenoxy)pyrimidine (prepared asabove) were suspended in 10 ml conc. HCl and stirred at 80° C. for 1hour. After cooling to room temperature, the solution was made basicwith NaOH and extracted twice with 50 ml ethyl acetate. The combinedorganic layers were dried over Na₂ SO₄, evaporated and the residue waspurified on silica gel with toluene/ethyl acetate as eluent to give 1.8g (31.8%) of 4-(3-trifluoromethylphenoxy)pyrimindine-4-carbamide of m.p.107° C. The alkaline water layer was acidified with conc. HCl andextracted three times with 50 ml ethyl acetate. The combined ethylacetate layers were dried over Na₂ SO₄ and evaporated to dryness to give0.44 g (7.8%) of 4-(3-trifluoromethylphenoxy)pyrimidine-2-carboxylicacid, m.pt. 143° C. (with decomposition).

Compound14--4-(3-trifluoromethylphenoxy)pyrimidine-2-N-(4-fluorophenyl)carboxamide

Analogously to the preparation of Compound 42-(3-trifluoromethylphenoxy)pyrimidine-4-(N-(4-fluorophenyl))carboxamide!0.44g of 4-(3-trifluoromethylphenoxy)pyrimidine-2-carboxylic acid gave,after purification on silica gel with toluene/ethyl acetate as eluent,0.41 g (70.7%) of pure4-(3-trifluoromethylphenoxy)-pyrimidine-2-(N-(4-fluorophenyl))carboxamide as white crystals of m.p. 113° C.

EXAMPLE 4 Preparation of4-(trifluoromethyl)phenoxy-6-(N,N-dimethylamino)pyrimidine-2-(N-(4-fluorophenyl))carboxamide

Compound 15--2-methylthio-4-chloro-6-(N,N-dimethylamino) pyrimidine

To a solution of 46 g 2-methylthio-4,6-dichloropyrimidine in 250 mldioxane, were added at room temperature and over a period of 10 minutes,65.6 ml of 40% dimethylammonia-solution in water and the mixture wasstirred for one hour. The solvent was evaporated and the residuepurified on silica gel with toluene as eluent to give 57.0 g (97.9%) of2-methylthio-4-chloro-6-(N,N-dimethylamino)-pyrimidine of m.p. 102° C.

Compound16--2-methylthio-4-(3-trifluoromethyl)phenoxy-6-(N,N-dimethylamino)pyrimidine

A solution of 8.1 g of 3-trifluoromethylphenol and 9.0 g NaOCH₃-solution (30%) in 200 ml toluene was stirred for 20 minutes and themixture was evaporated to dryness. The residue was dissolved in 20 mldimethylsulphoxide and 10.18 g of2-methylthio-4-chloro-6-(N,N-dimethylamino)pyrimidine (prepared asabove) were added and the solution was stirred for 18 hours at 135° C.After cooling to room temperature the solution was poured into 200 ml ofwater and extracted twice with 50 ml of ethyl acetate. The combinedethyl acetate layers were dried over Na₂ So₄ and evaporated to dryness.The residue was purified on silica gel with toluene as eluent to give14.48 g (88%) of pure2-methylthio-4-(3-trifluoro-methyl)phenoxy-6-(N,N-dimethylamino)-pyrimidineof m.p. 108° C.

Compound 16(A). Following similar procedure,2-methylthio-4-(2-chloropyrid-4-yloxy)-6-(N,N-dimethylamino)-pyrimidinewas prepared in 45.2% yield; m.pt. 98°-99° C.

Compound17--2-Methylsulfonyl-4-(3-trifluoromethyl)phenoxy-6-(N,N-dimethylamino)pyrimidine

3.3 g of2-methylthio-4-(3-trifluoromethyl)phenoxy-6-(N,N-di-methylamino)pyrimidine(prepared as above) were dissolved in 50 ml trichloromethane and 5 g ofm-chloroperbenzoic acid were added over a period of 5 minutes at 0° C.The mixture was stirred for 15 minutes and allowed to come to roomtemperature. The precipitated m-chlorobenzoic acid was filtered off andwashed with 20 ml of trichloromethane. The filtrate was reduced and theresidue was purified on silica gel with toluene/ethyl acetate as eluentto give 13.5 g (94.9%) of pure2-methylsulfonyl-4-(3-trifluoromethyl)-phenoxy-6-(N,N-dimethylamino)pyrimidineof m.p. 91°-92° C.

Compound 17(A). Following a similar procedure,2-methylsulphonyl-4-(2-chloropyrid-4-yloxy)-6-(N,N-dimethyl-amino)-pyrimidinewas prepared in 54.7% yield; m.pt. 89° C.

Compound18--2-Cyano-4-(3-trifluoromethyl)phenoxy-6-(N,N-dimethyl-amino)pyrimidine

1.7g of2-methylsulfonyl-4-(3-trifluoromethyl)phenoxy-6-(N,N-dimethylamino)pyrimidine(prepared as above) and 0.3 g of KCN were dissolved in 8 mldimethylformamide and the mixture was stirred at 110° C. for 45 minutes.After cooling to room temperature the mixture was poured into 100 ml ofwater and was extracted twice with 50 ml ethyl acetate. The combinedorganic layers were dried over Na₂ SO₄ and evaporated. The residue waspurified on silica gel with toluene as eluent to give 1.1 g (75.9%) of2-cyano-4-(3-tri- fluoromethyl)phenoxy-6-(N,N-dimethylamino)pyrimidineof m.p. 88°-92° C.

Compound 18(A). Following a similar procedure,2-cyano-4-(2-chlorpyrid-4-yloxy)-6-(N,N-dimethylamino)pyrimidine wasprepared in 40.8% yield; pt. 98°-108° C.

Compound19--4-(trifluoromethyl)phenoxy-6-(N,N-dimethylamino)-pyrimidine-2-carboxylicacid 2.5 g NaOH were dissolved in 50 ml water and 4.5 g of2-cyano-4-(3-trifluoromethyl)phenoxy-6-(N,N-dimethylamino)pyrimidine(prepared as above) were added and the mixture was refluxed for 5 hours.After cooling the mixture was extracted twice with 20 ml ethyl acetateand the alkaline aqueous solution was acidified with glacial aceticacid. The acid water solution was extracted four times with 50 ml ethylacetate and the combined organic layers were dried over Na₂ SO₄ andevaporated to give 3.8 g (77.4%) of pale yellow crystals of4-(trifluoromethyl)phenoxy-6-(N,N-dimethylamino)pyrimidine-2-carboxylicacid of m.p. 110°-114° C.

Compound20--4-(Trifluoromethyl)phenoxy-6-(N,N-dimethylamino)-pyrimidine-2-(N-(4-fluorophenyl))carboxamide

0.98 g of 4-(trifluoromethyl)phenoxy-6-(N,N-dimethylamino)-pyrimidine-2-carboxylic acid (prepared as above) were dissolved in 2 mlof SOCl₂ and refluxed for 10 minutes. The solution was evaporated and 10ml of toluene were added and the mixture stirred for 5 minutes andevaporated again. The residue was dissolved in 20 ml of toluene and asolution of 0.6 g triethylamine and 0.34 g of 4-fluoroaniline in 20 mlof toluene was added and the mixture was stirred for 15 minutes at roomtemperature. After pouring into 100 ml water the organic layer wasseparated and the water phase was extracted twice with 75 ml of toluene.The combined organic layers were extracted twice with 20 ml of dil. HCland once with 50 ml of water, dried over Na₂ SO₄ and evaporated todryness. The residue was purified on silica gel with toluene/ethylacetate to give 0.81 g (64.3%) of4-(trifluoromethyl)phenoxy-6-(N,N-dimethyl-amino)pyrimidine-2-(N-(4-fluorophenyl))carboxamideof m.p. 148°-149° C.

Compound 20(A). Following a similar procedure,4-(2-chloropyrid-4-yloxy)-6-(N,N-dimethylamino)pyrimidine-2-(N-(4-fluorophenyl))carboxamidewas prepared in 91.1% yield; m.pt. 157°-163° C.

EXAMPLE 5

Table 2 contains compounds synthesised according to the procedure ofExample 4.

                  TABLE 2                                                         ______________________________________                                         ##STR15##                                                                    Compound                                                                      No.     R.sub.1  R.sub.2      m.p. (°C.)                                                                    yield (%)                                ______________________________________                                        21      H        2,4-di-FC.sub.6 H.sub.3                                                                    141    64.7                                     22      H        C.sub.6 H.sub.5                                                                             93    75.5                                     23      C.sub.2 H.sub.5                                                                        C.sub.6 H.sub.5                                                                            oil    79.9                                     24      H        H            216    15.3                                     ______________________________________                                         Compound 23 NMR (CDCl.sub.3): 1.3(t, 3H, CH.sub.3); 3.0(s, 6H,                N(CH.sub.3).sub.2); 3.8(q, 2H, CH.sub.2); 5.6(s, 1H); 6.9-7.4(m, 9H,          Arom.).                                                                  

EXAMPLE 6 Preparation of6-(3-trifluoromethyl)phenoxypyrazine-2-(N-(4-fluorophenyl)carboxamide

Compound 25--Ethyl pyrazine carboxylate

To 20 g of pyrazine carboxylic acid were added 25 ml of SOCl₂ and themixture was refluxed for 30 minutes, evaporated, the residue wasdissolved in 30 m. of toluene and evaporated again.

The residue was dissolved in 50 ml toluene and dropped into 150 mlethanol over a period of 30 minutes and the resulting mixture wasstirred overnight at room temperature. Evaporation and filtration onsilica gel with ethyl acetate yielded 23.3 g (93.9%) of an orange oilwhich solidified overnight to crystals of m.p. 45° C.

Compound 26--Ethyl pyrazine carboxylate-4-oxide 3.4 g hydrogen peroxide(30%) was added in three portions over a period of 1 hour to a solutionof 3.06 g of ethyl pyrazine carboxylate (prepared as above) in 15 ml ofglacial acetic acid at 65° C. After stirring for 16 hours another 3.4 ghydrogen peroxide were added and the solution was stirred for 48additional hours. The volume of the mixture was reduced, 30 ml ofethanol were added and the solution was filtered. The liquid wasevaporated and the residue purified on silica gel with toluene/ethylacetate to give 0.5 g (14.80) of white ethylpyrazinecarboxylate-4-oxide; m.pt. 128° C.

Compound 27--Ethyl 6-chloropyrazine-2-carboxylate

2.3 g of ethyl pyrazine carboxylate-4-oxide (prepared as above), 12 mlPOCl₃ and 20 ml of toluene were mixed and stirred for 1 hour at 90°-100°C. After cooling 50 ml of ice water were added, the solution was madebasic with sufficient Na₂ SO₃ solution and extracted twice with 30 mlethyl acetate. The combined organic layers were dried over Na₂ SO₄ andevaporated to give 2.5 g (100%) of a dark brown oil which was used forfurther reaction without purification.

NMR(CDCl₃):1.45(t,3H,CH₃); 4.5(q,2H,CH₂); 8.8(s,1H, Arom.); 9.2(s,1H,Arom.)

Compound 28--Ethyl 6-(3-trifluoromethyl)-henoxyoyrazine-2-carboxylate

To a solution of 2.87 g sodium phenolate in 30 ml dimethyl-formamidewere added 2.9 g ethyl 6-chloropyrazine-2-carboxylate (prepared asabove) and the mixture was stirred for 1 hour at 80° C. Afterevaporation the residue was diluted with water and extracted twice with50 ml ethyl acetate. The combined organic layers were dried over Na₂ SO₄evaporated, and the residue was separated on silica gel withpetroleum/methyl tert.butyl ether to give 3.95 g (81.4%) of whitecrystals, m.p. 80.50° C.--Compound 27.

Analogous to the above procedure, the compounds in Table 3 have beenprepared

                  TABLE 3                                                         ______________________________________                                         ##STR16##                                                                    Compound                                                                      No.      R               R.sub.1 mp °C.                                                                       % yield                                ______________________________________                                        29       1-CH.sub.3 -3-CF.sub.3 -pyrazol-5-yl                                                          C.sub.3 H.sub.9                                                                       74    63.3                                   30       3-CF.sub.3 -4-FC.sub.6 H.sub.4                                                                C.sub.2 H.sub.5                                                                       69-1  18.9                                   ______________________________________                                    

Compound 31--6-(3-Trifluoromethyl)phenoxypyrazine-2-carboxylic acid

4.92 g of ethyl 6-(3-trifluoromethyl)phenoxy-yrazine-2-carboxylate weredissolved in 40 ml ethanol, 8.5 ml of 2N NaOH were added and the mixturewas refluxed for 1 hour. After cooling the solvent was distilled off,the residue was dissolved in 5 ml water and the solution was acidifiedwith 2N HCl. The precipitate was separated by filtration to give 3.7 g(92.5%) of white crystals of m.p. 118° C.

Following the above procedure, analogous compounds listed in Table 4have been prepared.

                  TABLE 4                                                         ______________________________________                                         ##STR17##                                                                    Compound                                                                      No.     R               R.sub.1                                                                              mp °C.                                                                        % yield                                 ______________________________________                                        32      1-CH.sub.3 -3-CF.sub.3 -pyrazol-5-yl                                                          H      126-136                                                                              79.0                                    33      3-CF.sub.3 -4-FC.sub.6 H.sub.4                                                                H      117    70.9                                    ______________________________________                                    

Compound34--6-(3-trifluoromethyl)-phenoxypyrazine-2-(N-(4-fluorophenyl))carboxamid

To 1.07 g of 6-(3-trifluoromethyl)phenoxy-yrazine-2-carboxylic acidchloride (prepared from 1 g acid and 5 ml SOCl₂) were added a solutionof 0.5 g 4-fluoroaniline and 0.36 g of triethylamine in 10 ml toluene atroom temperature and the mixture was stirred for 15 minutes. 50 ml ofethyl acetate and 50 ml of water were added, the organic layer wasseparated and washed first with 50 ml dil. HCl and then with 50 ml 0.5NNaOH. After drying over Na₂ SO ₄ and evaporation to dryness, 1.23 g(92.6%) of slightly yellow crystals of Compound 29 were collected; m.p.91° C.

EXAMPLE 6(A)

Table 5 contains details of further compounds synthesised according tothe procedure of Example 6.

                  TABLE 5                                                         ______________________________________                                         ##STR18##                                                                    Compound                                                                      No.     R.sub.1                                                                              R.sub.2        m. pt. (°C.)                                                                   yield (%)                               ______________________________________                                        35      H      2,4-di-FC.sub.6 H.sub.3                                                                      111     95.9                                    36      C.sub.2 H.sub.5                                                                      C.sub.6 H.sub.5                                                                               55     93.0                                    37      H      2-FC.sub.6 H.sub.4                                                                           136     90.4                                    38             CH.sub.2 CH.sub.2 OCH.sub.2 CH.sub.2                                                         107-110 38.0                                    ______________________________________                                    

In analogy to the procedure for compound 34, the following compoundslisted in Table 6 have been prepared.

                                      TABLE 6                                     __________________________________________________________________________     ##STR19##                                                                    Compound                                                                      No.    R          R.sub.1  R.sub.2                                            __________________________________________________________________________    39     3-CF.sub.3C.sub.6 H.sub.4                                                                H        C.sub.6 H.sub.5                                    40     3-CF.sub.3C.sub.6 H.sub.4                                                                C.sub.6 H.sub.5                                                                        C.sub.6 H.sub.5                                    41     3-CF.sub.3C.sub.6 H.sub.4                                                                H                                                           3-FC.sub.6 H.sub.4                                                            42     3-CF.sub.3C.sub.6 H.sub.4                                                                CH.sub.2 CHCH.sub.2                                                                    C.sub.6 H.sub.5                                    43     3-CF.sub.3C.sub.6 H.sub.4                                                                H                                                           4-OC.sub.6 H.sub.5C.sub.6 H.sub.4                                             44     3-CF.sub.3C.sub.6 H.sub.4                                                                H                                                           cyclo-C.sub.3 H.sub.5                                                         45     3-CF.sub.3C.sub.6 H.sub.4                                                                H                                                           i-C.sub.3 H.sub.7                                                             46     3-CF.sub.3C.sub.6 H.sub.4                                                                H        CH.sub.2 CHCH.sub.2                                47     3-CF.sub.3C.sub.6 H.sub.4                                                                H                                                           n-C.sub.4 H.sub.9                                                             48     3-CF.sub.3C.sub.6 H.sub.4                                                                H        C(CH.sub.3).sub.3                                  49     3-CF.sub.3C.sub.6 H.sub.4                                                                H                                                           cyclo-C.sub.4 H.sub.7                                                         50     3-CF.sub.3C.sub.6 H.sub.4                                                                H                                                           2-Cl-pyrid-4-yl                                                               51     3-CF.sub.3C.sub.6 H.sub.4                                                                H                                                           n-C.sub.3 H.sub.7                                                             52     3-CF.sub.3C.sub.6 H.sub.4                                                                H        CH.sub.2 CF.sub.3                                  53     3-CF.sub.3C.sub.6 H.sub.4                                                                H                                                           3,5-FC.sub.6 H.sub.3                                                          54     3-CF.sub.3C.sub.6 H.sub.4                                                                H        C(CH.sub.3).sub.2 CCH                              55     3-CF.sub.3C.sub.6 H.sub.4                                                                H        CH.sub.2 -cyclo-C.sub.3 H.sub.5                    56     1-CH.sub.3 -3CF.sub.3 -pyrazol-5-yl                                                      H                                                           4-FC.sub.6 H.sub.4                                                            57     1-CH.sub.3 -3CF.sub.3 -pyrazol-5-yl                                                      H                                                           3-FC.sub.6 H.sub.4                                                            58     1-CH.sub.3 -3CF.sub.3 -pyrazol-5-yl                                                      H        C.sub.6 H.sub.5                                    59     1-CH.sub.3 -3CF.sub.3 -pyrazol-5-yl                                                      H                                                           cyclo-C.sub.3 H.sub.5                                                         60     1-CH.sub.3 -3CF.sub.3 -pyrazol-5-yl                                                      H                                                           cyclo-C.sub.4 H.sub.7                                                         61     1-CH.sub.3 -3CF.sub.3 -pyrazol-5-yl                                                      H                                                           n-C.sub.4 H.sub.9                                                             62     1-CH.sub.3 -3CF.sub.3 -pyrazol-5-yl                                                      H                                                           2,4-FC.sub.6 H.sub.3                                                          63     1-CH.sub.3 -3CF.sub.3 -pyrazol-5-yl                                                      H        CH.sub.2 CF.sub.3                                  64     1-CH.sub.3 -3CF.sub.3 -pyrazol-5-yl                                                      H                                                           cyclo-C.sub.6 H.sub.11                                                        65     1-CH.sub.3 -3CF.sub.3 -pyrazol-5-yl                                                      H                                                           cyclo-C.sub.5 H.sub.9                                                         66     1-CH.sub.3 -3CF.sub.3 -pyrazol-5-yl                                                      CH.sub.3 C.sub.6 H.sub.5                                    67     1-CH.sub.3 -3CF.sub.3 -pyrazol-5-yl                                                      H                                                           1,2,4-triazole-1-yl                                                           68     1-CH.sub.3 -3CF.sub.3 -pyrazol-5-yl                                                      H                                                           1,2,4-triazole-2-yl                                                           69     1-CH.sub.3 -3CF.sub.3 -pyrazol-5-yl                                                      H        3,5-FC.sub.6 H.sub.3                               70     1-CH.sub.3 -3CF.sub.3 -pyrazol-5-yl                                                      H        CH.sub.2 -cyclo-C.sub.3 H.sub.5                    71     1-CH.sub.3 -3CF.sub.3 -pyrazol-5-yl                                                      H        CH(CH.sub.3)CH.sub.2 CH.sub.3                      72     1-CH.sub.3 -3CF.sub.3 -pyrazol-5-yl                                                      H                                                           3,4-FC.sub.6 H.sub.3                                                          73     1-CH.sub.3 -3CF.sub.3 -pyrazol-5-yl                                                      H        OC(CH.sub.3).sub.3                                 74     1-CH.sub.3 -3CF.sub.3 -pyrazol-5-yl                                                      H        morpholin-1-yl                                     75     1-CH.sub.3 -3CF.sub.3 -pyrazol-5-yl                                                      H        hexamethylenimin-1-yl                              76     1-CH.sub.3 -3CF.sub.3 -pyrazol-5-yl                                                      CH.sub.3 CH.sub.3                                           77     1-CH.sub.3 -3CF.sub.3 -pyrazol-5-yl                                                      CH.sub.2CH.sub.3                                                                       C.sub.6 H.sub.5                                    78     1-CH.sub.3 -3CF.sub.3 -pyrazol-5-yl                                                      CH.sub.2CH.sub.2CH.sub.3                                                               CH.sub.2CH.sub.2CH.sub.3                           79     1-CH.sub.3 -3CF.sub.3 -pyrazol-5-yl                                                      CH.sub.2CH.sub.2CH.sub.3                                    3,4-FC.sub.6 H.sub.3                                                          80     1-CH.sub.3 -3CF.sub.3 -pyrazol-5-yl                                                      CH.sub.2 CHCH.sub.2                                                                    C.sub.6 H.sub.5                                    81     1-CH.sub.3 -3CF.sub.3 -pyrazol-5-yl                                                      CH.sub.2 C.sub.6 H.sub.5                                                               CH.sub.6 H.sub.5                                   82     1-CH.sub.3 -3CF.sub.3 -pyrazol-5-yl                                                      CH.sub.2 C.sub.6 H.sub.5                                                               pyridyl-2-yl                                       83     1-CH.sub.3 -3CF.sub.3 -pyrazol-5-yl                                                      2-CH.sub.3 -aziridin-1-yl                                   84     1-CH.sub.3 -3CF.sub.3 -pyrazol-5-yl                                                      H                                                           2-FC.sub.6 H.sub.4                                                            85     1-CH.sub.3 -3CF.sub.3 -pyrazol-5-yl                                                      H        CH.sub.2CH.sub.2CH.sub.3                           86     3-CF.sub.3 -4-F-C.sub.6 H.sub.3                                                          H                                                           4-FC.sub.6 H.sub.4                                                            87     3-CF.sub.3 -4-F-C.sub.6 H.sub.3                                                          H        C.sub.6 H.sub.5                                    __________________________________________________________________________

Compound88--6-(1-Methyl-3-trifluoromethylpyrazol-5-yloxy)-pyrazine-6-((N-methyl)(N-cyclopropyl)carboxamide

0.12g (4mmol) NaH were added at room temperature to a solution of 0.92g(2,8mmol) of compound 59 in 30 ml THF. After stirring for 15 min at 50°C. 1 ml of iodomethane was added and the resulting mixture as refluxedfor 2 hours. After cooling 2 ml of water were added, the solvent wasevaporated and the residue was solved in 10 ml of ethylacetate, washedwith water and dried over Na₂ SO₄. The solvent was evaporated and theresidue was purified on silica gel using toluene/ethylacetate (2/1) aseluent to give 0.80 g (83.4%) of a brown oil.

NMR(CDCl₃): 0.3-0.5(m,4H,CH₂); 2.75(m,1H,CH); 3.13(s,3H, CH₃); 6.33(S,1H, arom); 8.62(s. 1H, arom); 8.73(s, 1H arom);

Compounds of Table 7 have been prepared according to the procedure usedfor compound 88.

                  TABLE 7                                                         ______________________________________                                         ##STR20##                                                                    Compound                                %                                     No.     R.sub.1       R.sub.2    m.p. °C.                                                                      yield                                 ______________________________________                                        89      CH.sub.3      2-FC.sub.6 H.sub.4                                                                       oil    78.3                                  90      CH.sub.3      3-FC.sub.6 H.sub.4                                                                       100-104                                                                              57.9                                  91      CH.sub.3      4-FC.sub.6 H.sub.4                                                                       104-108                                                                              54.0                                  92      CH.sub.3      2,4-FC.sub.6 H.sub.3                                                                     oil    67.2                                  93      CH.sub.3      3,4-FC.sub.6 H.sub.3                                                                     oil    49.8                                  94      CH.sub.3      CH.sub.2 CF.sub.3                                                                        oil    37.4                                  95      C.sub.2 H.sub.5                                                       n-C.sub.3 H.sub.7                                                                     oil           43.3                                                    96      C.sub.2 H.sub.5                                                                             cyclo-C.sub.3 H.sub.5                                                                    oil    46.1                                  97      C.sub.2 H.sub.5                                                                             4-FC.sub.6 H.sub.4                                                                       oil    39.2                                  98      C.sub.2 H.sub.5                                                                             3,4-FC.sub.6 H.sub.3                                                                     oil    36.8                                  99      CH.sub.2 CH.sub.2 CH.sub.3                                            3,4-FC.sub.6 H.sub.3                                                                  oil           75.1                                                    100     CH.sub.2 CHCH.sub.2                                                                         cyc1o-C.sub.3 H.sub.5                                                                    oil    18.7                                  101     CH.sub.2 CHCH.sub.2                                                                         4-FC.sub.6 H.sub.4                                                                       oil    47.1                                  102     CH.sub.2 CHCH.sub.2                                                                         3,4-FC.sub.6 H.sub.3                                                                     oil    41.6                                  ______________________________________                                    

EXAMPLE 7 Preparation of4-(3-trifluoromethyl)phenoxy-6-methylthio-1,3,5-triazine-2-(N-ethyl-N-phenyl)carboxamideCompound 30-3-Trifluoromethylphenylcyanate

To an ice cold solution of 10 g 3-trifluoro-ethylphenol 250 ml acetonewas added a solution of 6.54 g cyanogen bromide in 50 ml acetone and theresulting mixture was stirred for half an hour at 0° C. 6.25 gtriethylamine were mixed with 20 ml acetone and added to the mixture andthe resulting solution was stirred for another hour while warming toroom temperature. The suspension was filtered and the mother liquorevaporated. The residue was dissolved in 50 ml of toluene and theprecipitate was filtered off. The filtrate was evaporated to dryness togive 11.3 g (98.2%) of a pale yellow oil.

N-ethyl-N-phenyl-oxalic acid half anilide half chloride

To an ice cold solution of 4 g oxalylchloride in 60 toluene was added asolution of 3.81 g N-ethylaniline and 3.19 g triethylamine in 20 mltoluene over a period of 5 minutes and the resulting mixture was stirredfor half an hour while maintaining the temperature at 0° C. Thesuspension was filtered, the residue was washed with 10 ml of ice coldtoluene and the filtrate was evaporated to give 5 g (75.7%) of a brownoil, which was used for further reaction without any purification andisolation.

Compound104--4-(3-trifluoromethyl)phenoxy-6-methylthio-1,3,5-triazine-2-(N-ethyl-N-phenyl)carboxamide

To a solution of 5 g N-ethyl-N-phenyl-oxalyl half chloride half anilide(prepared as above) in 60 ml of dioxane was added a solution of 4.42 g3-trifluoromethylphenyl cyanate over a period of 20 minutes and theresulting mixture was stirred for 2 hours at 50° C. After cooling to 10°C., 2.13 g isothiourea were added in one portion, followed by a solutionof 4.78 g triethylamine in 50 ml dioxane. The mixture was stirredovernight at room temperature, filtered and the liquid evaporated todryness.

The residue was dissolved in 250 ml ethyl acetate, washed twice with 50ml dil. HCl, 50 ml water, twice with 50 ml dil. NaOH and again with 50ml water. The organic layer was dried over Na₂ SO₄ and evaporated. Theresidue was purified on silica gel with petroleum/ethyl acetate aseluent to give 0.18 g (1.75%, based on cyanate) of a yellow oil,identified as Compound 104.

EXAMPLE 8 Preparation of2-(3-trifluoromethyl)phenoxy-6-methyl-pyrimidine-4-(N-(4-fluorophenyl))carboxamide

Compound 32--2-Chloro-4-cyano-6-methylpyrimidine

24.5 g of 2,4-dichloro-6-methylpyrimidine and 9.8 g of potassium cyanidewere dissolved in 150 ml of CH₃ CN and refluxed for 8 days. The solventwas evaporated, the residue was dissolved in 150 ml of ethyl acetate andextracted twice with 50 ml H₂ O. The organic layer was dried over Na₂SO₄, the solvent was evaporated and the residue was purified on silicagel using a 4:1 mixture of benzene and methyl tert.butyl ether as eluentto give 5.2 g (24.8%) of 2-chloro-4-cyano-6-methyl pyrimidine of m.p.57° C.

Compound 106--2-(3-Trifluoromethyl)phenoxy-4-cyano-6-methyl-pyrimidine

5.1 g of compound 32 (prepared as above) and 6.73 g of3-trifluoromethylphenol sodium salt were dissolved in 20 mldimethylformamide and stirred for 4 hours at 110° C. The solvent wasevaporated and the residue was dissolved in 50 ml H₂ O and the aqueousphase was extracted three times with 100 ml of of ethyl acetate. Thecombined organic layers were dried over Na₂ SO₄, the solvent wasevaporated and the residue was purified on silica gel with toluene/ethylacetate as eluent to give 3.36 g (38.8%) of compound 33 with m.pt.84°-86° C.

Compound107--2-(3-Trifluoromethyl)phenoxy-6-methylpyrimidine-4-carboxylic acid

3.36 g of 2-(3-trifluoromethyl)phenoxy-4-cyano-6-methyl-pyrimidine werestirred in 20 ml of half conc. HCl for one hour at 80° C., diluted with100 ml H₂ O and extracted twice with 100 ml of ethyl acetate. Theorganic layer was dried over Na₂ SO₄, the solvent was evaporated and theresidue was purified on silica gel using ethyl acetate followed bymethanol as eluent to give 1.78 g (49.6%) of compound 34 (contaminatedwith silica gel) of m.p. >250° C.

Compound108--2-(3-Trifluoromethyl)phenoxy-6-methylpyrimidine-4-(N-(4-fluorophenyl))carboxamide

1.77 g of compound 34 (prepared as above) were refluxed for 30 minutesin 5 ml of SOCl₂ and evaporated to dryness after cooling. The residuewas dissolved in 50 ml toluene, evaporated and dissolved again in 50 mltoluene. This solution was added dropwise to a solution of 0.66 g4-fluoroaniline and 0.6 g triethylamine in 5 ml toluene and stirred for1 hour room temperature. The solution was extracted twice with 25 mlwater. The water layer was extracted with 25 ml of dil. HCl, followed by25 ml of dil. NaOH and then with 50 ml water. The organic layers werecombined and dried over Na₂ SO. The solvent was evaporated and theresidue was purified on silica gel with toluene/ethyl acetate to give0.4 g (17.2%) of compound 35 as a brown oil.

NMR (CDCl₃): 2.65(s,3H,CH₃); 6.9(s,1H,Arom.); 7.0(m,2H,Arom.);

7.4(m,1H,Arom.); 7.5(m,1H,Arom.), 7.6(m,4H,Arom.); 9.5(s,1H,NH).

Compound109--2-Thiomethyl-4-(2-chloropyrid-4-yloxy)-6-(N,N-dimethylamino)pyrimindine

According to the procedure for compound 16, compound 109 has beenprepared in 45.2% with m.p. 98°-99° C.

Compound110--2-Methylsulfonyl-yl-4-(2-chloropyrid-4-yloxy)-6-(N,N-dimethylamino)pyrimidine

Following the procedure for compound 17, compound 110 has been preparedin 54.7% yield with m.p. 89° C.

Compound111--2-Cyano-4-(2-chloropyrid-4-yloxy)-6-(N,N-dimethylamino)pyrimidine

According to the procedure described for compound 18, compound 111 hasbeen prepared in 40.8% with m.p. 98°-108° C.

Compound112--4-(2-chloropyrid-4-yloxy)-6-(N,N-dimethylamino)-pyrimidine-2-(N-(4-fluorophenyl)carboxamide

Compound 112 has been prepared following the procedure for compound 20in 91.1% with m.p. 157°-163° C.

                  TABLE 8                                                         ______________________________________                                        Elemental Analysis                                                                   Calc.         Found                                                    Compound No.                                                                           C (%)   (H (%)  N (%) C (%) H (%) N (%)                              ______________________________________                                         1       54.35   2.28    15.85 52.67 3.49  13.65                               2       50.89   2.85    14.84 51.18 3.19  14.43                               3       50.72   2.48    9.86  48.96 2.96  13.91                               4       55.25   2.83    14.32 57.25 3.13  11.10                               5       60.17   3.37    11.69 59.08 3.75  11.13                               6       62.01   4.16    10.85 62.59 4.57  10.37                               7       56.64   4.75    12.38 56.78 4.69  12.26                               8       54.69   2.55    10.63 55.11 3.17  10.46                               9       55.79   3.74    13.00 55.93 3.96  12.63                               10      55.24   2.53    11.71 54.97 2.76  11.09                               11      54.35   2.28    15.85 54.11 2.26  15.55                               12      50.89   2.85    14.84 51.06 3.04  15.76                               13      50.72   2.48    9.86  49.98 3.13  9.75                                14      57.30   2.94    11.14 57.24 2.98  11.25                               15      41.28   4.95    20.63 41.30 4.87  20.25                               16      51.05   4.28    12.75 50.58 4.28  13.42                               17      46.54   3.90    11.63 47.41 4.20  10.74                               18      54.55   3.60    18.18 54.83 3.99  18.74                               19      51.38   3.70    12.84 51.09 3.73  12.93                               20      57.15   3.84    13.33 57.15 4.31  13.23                               21      54.80   3.45    12.78 54.90 4.17  12.73                               22      59.70   4.26    13.92 58.32 4.89  13.47                               23      61.39   4.92    13.92 61.67 5.32  12.51                               25      55.26   5.30    18.41 54.21 5.34  17.60                               26      50.00   4.79    16.66 49.63 4.73  15.97                               28      53.85   3.55    8.97  53.69 3.48  8.82                                31      50.72   2.48    9.86  50.95 2.86  10.20                               34      55.25   2.83    14.32 57.95 2.86  10.20                              103      51.35   2.15    7.49  51.53 2.89  7.13                               104      57.63   3.74    12.22 58.23 3.66  11.98                              105      51.61   2.87    20.07 50.89 2.56  20.56                              106      65.82   3.37    17.72 65.39 3.21  17.98                              107      60.94   3.51    10.94 60.65 3.73  10.04                              108      58.31   3.32    10.74 58.12 3.19  11.01                               24      51.49   3.98    17.16 51.03 4.29  17.39                               35      54.64   2.53    10.63 54.98 2.92  11.16                               36      61.96   4.13    10.84 61.84 4.37  10.92                               37      57.25   2.92    11.13 57.56 3.30  11.41                               38      54.39   3.99    11.89 54.23 4.06  11.78                               16a     48.57   4.41    18.88 48.37 4.12  18.66                               17a     43.84   3.98    17.04 43.64 3.65  16.59                               18a     52.28   3.66    25.40 52.46 3.96  25.42                               20a     55.75   3.90    18.06 55.82 4.00  17.14                              ______________________________________                                    

EXAMPLE 9 Herbicidal Activity

To evaluate their herbicidal activity, compounds according to theinvention were tested using as representative range of plants: maize,Zea mays (Mz); rice, Oryza sativa (R); barnyard grass, Echinochloacrusgalli (BG); oat, Avena sativa (O); linseed, Linum usitatissimum (L);mustard, Sinapsis alba (M); sugar beet, Beta vulgaris (SB) and soyabean, Glycine max (S).

The tests fall into two categories, pre-emergence and post-emergence.The pre-emergence tests involved spraying a liquid formulation of thecompound onto the soil in which the seeds of the plant species mentionedabove had recently been sown. The post-emergence tests involved twotypes of test, viz., soil drench and foliar spray tests. In the soildrench tests the soil in which the seedling plants of the above specieswere growing was drenched with a liquid formulation containing acompound of the invention, and in the foliar spray tests the seedlingplants were sprayed with such a formulation.

The soil used in the tests was a prepared horticultural loam.

The formulations used in the tests were prepared from solutions of thetest compounds in acetone containing 0.4% by weight of analkylphenol/ethylene oxide condensate available under the trade markTRITON X-155. These acetone solutions were diluted with water and theresulting formulations applied at dosage levels corresponding to 5 kg or1 kg of active material per hectare in a volume equivalent to 600 litersper hectare in the soil spray and foliar spray test, and at a dosage oflevel equivalent to 10 kilograms of active material per hectare in avolume equivalent to approximately 3,000 liters per hectare in the soildrench tests.

In the pre-emergence tests untreated sown soil and in the post-emergencetests untreated soil bearing seedling plants were used as controls.

The herbicidal effects of the test compounds were assessed visuallytwelve days after spraying the foliage and the soil, and thirteen daysafter drenching the soil and were recorded on a 0-9 scale. A rating 0indicates growth as untreated control, a rating 9 indicates death. Anincrease of 1 unit on the linear scale approximates to a 10% increase inthe level of effect.

The results of the tests are set out in Table 5 below, in which thecompounds are identified by reference to the preceding Compound Nos.allocated in Examples 1 to 8 above. Absence of a numeral indicates thatno test was carried out; an asterisk indicates that no result wasobtained.

                                      TABLE 5                                     __________________________________________________________________________    Compound                                                                            Soil drench 10 kg/ha                                                                          Dosage                                                                            Foliar spray    Pre-emergence                       No.   Mz                                                                              R BG                                                                              O L M SB                                                                              S kg/ha                                                                             Mz                                                                              R BG                                                                              O L M SB                                                                              S Mz                                                                              R BG                                                                              O L M SB                                                                              S                     __________________________________________________________________________     2    3 0 4 3 0 4 2 0 5   0 0 4 0 2 4 2 5 0 0 0 0 0 3 0 0                                           1   0 0 0 0 0 0 0 4 0       0                                                                             0                                                                             0                                                                             0 0 0 0                      3    0 0 0 0 0 0 0 0 5   0 0 2 0 3 4 3 5 0       0                                                                             0                                                                             0                                                                             0 0 0 0                                           1   0 0 0 0 0 2 0 2 0       0                                                                             0                                                                             0                                                                             0 0 0 0                      4    4 0 5 4 3 4 2 0 5   5 0 8 5 6 8 9 6 2       0                                                                             5                                                                             2                                                                             4 9 8 4                                           1   4 0 7 2 6 7 9 4 0       0                                                                             2                                                                             0                                                                             0 8 7 0                      5    0 0 0 0 0 3 0 0 5   5 0 7 3 5 9 9 6 1       0                                                                             3                                                                             0                                                                             0 8 8 0                                           1   2 0 4 0 4 8 8 5 0       0                                                                             1                                                                             0                                                                             0 7 6 0                      6    0 0 0 0 0 3 0 0 5   4 0 3 2 4 9 9 5 0       0                                                                             0                                                                             0                                                                             0 6 6 2                                           1   2 0 2 0 3 8 8 4 0       0                                                                             0                                                                             0                                                                             0 5 2 0                      7    0 0 0 0 0 0 0 0 5   4 0 3 2 3 7 6 4 0       0                                                                             0                                                                             0                                                                             0 2 2 0                                           1   2 0 0 0 0 6 4 2 0       0                                                                             0                                                                             0                                                                             0 1 1 0                      8    0 0 0 0 0 0 0 0 5   4 0 4 3 6 8 9 7 0       0                                                                             4                                                                             0                                                                             0 7 7 2                                           1   2 0 3 2 2 8 7 5 0       0                                                                             2                                                                             0                                                                             0 7 6 0                      9    0 0 0 0 0 5 3 2 5   4 0 6 4 4 8 8 4 3       0                                                                             4                                                                             2                                                                             0 4 8 2                                           1   2 0 2 0 2 6 6 2 0       0                                                                             2                                                                             0                                                                             0 2 3 0                     11    0 0 0 0 0 0 0 0 5   5 0 2 0 2 4 4 3 0       0                                                                             0                                                                             0                                                                             0 0 0 0                                           1   0 0 0 0 0 2 0 0 0       0                                                                             0                                                                             0                                                                             0 0 0 0                     14    0 0 0 0 0 0 0 0 5   6 0 8 4 6 9 9 5 2       0                                                                             3                                                                             2                                                                             3 8 4 0                                           1   4 0 4 2 5 8 9 4 0       0                                                                             2                                                                             0                                                                             0 8 2 0                     18      * * * * * *   5     4 2 0 4 7 6           0                                                                             2                                                                             1                                                                             0 4 5                                             1     2 0 0 2 5 3           0                                                                             0                                                                             0                                                                             0 3 2                       19    0 0 0 0 0 0 0 0 5   0 0 2 0 0 8 0 0 0       0                                                                             0                                                                             0                                                                             0 2 0 0                                           1   0 0 0 0 0 7 0 0 0       0                                                                             0                                                                             0                                                                             0 0 0 0                     20    0 0 1 4 2 5 2 0 5   5 0 6 2 4 9 8 4 0       0                                                                             0                                                                             0                                                                             0 8 7 0                                           1   2 0 2 0 2 8 7 2 0       0                                                                             0                                                                             0                                                                             0 8 6 0                     21    0 0 0 4 0 4 2 0 5   0 0 0 0 0 7 6 0 0       0                                                                             0                                                                             0                                                                             0 6 4 0                                           1   0 0 0 0 0 7 5 0 0       0                                                                             0                                                                             0                                                                             0 6 2 0                     22    3 0 5 6 4 5 6 0 5   5 0 7 4 6 7 8 4 0       0                                                                             0                                                                             0                                                                             2 8 7 2                                           1   2 0 2 0 4 7 8 3 0       0                                                                             0                                                                             0                                                                             0 7 7 0                     23    4 0 5 1 2 4 2 0 5   5 0 6 1 2 6 8 4 0       0                                                                             1                                                                             0                                                                             0 7 8 2                                           1   1 0 2 0 0 5 8 2 0       0                                                                             0                                                                             0                                                                             0 7 8 0                     28    0 0 0 0 0 0 0 0 5   0 0 2 0 6 5 6 4 0       0                                                                             0                                                                             0                                                                             0 0 0 0                                           1   0 0 0 0 5 2 2 3 0       0                                                                             0                                                                             0                                                                             0 0 0 0                     29    4 0 6 2 3 6 2 0 5   6 6 8 7 6 8 9 8 2       0                                                                             7                                                                             2                                                                             2 5 6 0                                           1   5 4 7 6 5 8 9 7 0       0                                                                             6                                                                             0                                                                             0 4 4 0                     35    0 0 0 0 0 6 7 0 5   5 4 8 6 6 8 9 6 2       0                                                                             4                                                                             3                                                                             4 8 9 4                                           1   2 0 2 5 5 7 9 2 1       0                                                                             0                                                                             2                                                                             3 7 9 2                     36    4 0 5 0 2 6 5 4 5   0 0 6 2 6 8 8 7 0       0                                                                             7                                                                             0                                                                             5 8 8 5                                           1   0 0 2 0 5 8 7 6 0       0                                                                             2                                                                             0                                                                             2 6 5 4                     37    4 0 6 3 4 5 3 0 5   6 3 8 5 6 9 9 6 5       1                                                                             6                                                                             4                                                                             1 8 9 0                                           1   5 0 7 4 6 8 9 6 4       0                                                                             5                                                                             4                                                                             0 8 8 0                     38    4 0 3 4 5 7 8 0 5   4 0 8 6 7 8 9 7 0       0                                                                             7                                                                             0                                                                             2 8 8 0                                           1   2 0 5 4 6 8 8 6 0       0                                                                             2                                                                             0                                                                             0 8 8 0                     39    0 0 0 0 4 4 3 1 5   6 2 7 2 5 9 9 5 2       0                                                                             6                                                                             2                                                                             2 8 7 2                                           1   4 0 5 0 5 8 8 5 0       0                                                                             5                                                                             0                                                                             2 7 6 0                     16(A) 4 0 5 0 6 1 6 0 5   0 0 4 0 5 8 9 6 0       0                                                                             0                                                                             0                                                                             0 0 0 0                                           1   0 0 2 0 4 8 8 2 0       0                                                                             0                                                                             0                                                                             0 0 0 0                     18(A) 6 5 6 4 3 5 2 0 5   0 0 7 0 4 8 8 7 3       2                                                                             6                                                                             4                                                                             3 6 4 0                                           1   0 0 2 0 2 8 7 5 0       0                                                                             5                                                                             0                                                                             1 5 2 0                     __________________________________________________________________________

We claim:
 1. A compound of the formula (I) ##STR21## wherein Arepresents a group of formula ##STR22## in which the or each Xindependently represents a halogen atom or an optionally substitutedalkyl, alkoxy, phenyl or phenyloxy group or an alkenyloxy, alkynyloxy,alkylthio, haloalkylthio, alkenylthio, alkynylthio, alkylsulphinyl,alkylsulphonyl or cyano group, andn is 0 or an integer from 1 to 4, or,for the phenyl group, 5; or A represents a group of the formula##STR23## in which R⁴ represents a hydrogen or halogen atom or anoptionally substituted alkyl, alkenyl, alkynyl, cycloalkyl,cycloalkylalkyl, phenyl, phenylalkyl, alkylphenyl, alkoxy, amino, mono-or dialkylamino, alkoxycarbonylamino, phenylamino, dialkylcarbamoyl,acyl or acylamido group or a cyano group; each of R⁵ and R⁶independently represents a hydrogen or halogen atom or an optionallysubstituted alkyl, alkenyl, alkynyl, cycloalkyl, cycloalkylalkyl,phenyl, phenylalkyl, alkylphenyl, alkoxy, amino, mono- or dialkylamino,alkoxycarbonylamino, phenylamino, dialkylcarbamoyl group; Z representsan oxygen or atom; R¹ and R² each independently represent a hydrogenatom or an optionally substituted alkyl, alkenyl, alkynyl, cycloalkyl,cycloalkylalkyl, phenyl, phenylalkyl, alkylphenyl, hydroxyl, alkoxy,alkenyloxy, alkynyloxy, alkylcarbonyl, alkoxycarbonyl, amino, mono- ordialkylamino, alkoxycarbonylamino, phenylamino, phenylalkylamino ordialkylcarbamoyl group; or R¹ and R² together represent an alkylenechain having 3 to 6 chain members; R³ represents a hydrogen atom or anoptionally substituted alkyl, alkoxy, alkenyloxy, alkylthio or mono- ordialkylamino group; and Q² represents a nitrogen atom and Q³ representsCR³ ; in which any alkyl, alkenyl or alkynyl moiety which is or formspart of a group R¹, R², R³, R⁴, R⁵, R⁶ or X contains up to 12 carbonatoms, any cycloalkyl moiety which is or forms part of a group R¹, R²,R⁴, R⁵ or R⁶ contains 3 to 10 carbon atoms, any heterocyclyl moietywhich is or forms part of a group R¹ or R² is a single ring systemhaving 3 to 6 ring members selected from carbon atoms and at least onenitrogen, oxygen or sulfur atom; and in which optional substituents ofthe groups R¹, R², R⁴, R⁵, R⁶ or X are selected from the groupconsisting of halogen atoms, and phenyl, nitro, cyano, amino, hydroxyl,alkyl, alkoxy, mono- or dialkylamino groups, and haloalkyl, haloalkoxy,formyl alkoxycarbonyl carboxy, halophenyl groups and thienyl groups, inwhich any alkyl moiety of such optional substituents have 1 to 6 carbonatoms.
 2. A compound as claimed in claim 1, wherein A represents a group##STR24## in which X represents a halogen atom or a halo(C₁₋₂)alkylgroup and n is 0 or 1, orA represents a group ##STR25## in which R⁴ andR⁵ independently represents a C₁₋₄ alkyl group or a halo(C₁₋₂)alkylgroup.
 3. A compound as claimed in claim 1, wherein R¹ and R² eachindependently represents a hydrogen atom, a C₁₋₆ alkyl group, a C3-6cycloalkyl group or an unsubstituted or halo-substituted phenyl group.4. A compound as claimed in claim 1, wherein R³ represents a hydrogenatom, a C₁₋₄ alkyl group or a di(C₁₋₄)-alkylamino group.
 5. A compoundas claimed in claim 1, wherein A represents a 3-trifluoromethylphenylgroup, one of R¹ and R² represents a hydrogen atom or a C₁₋₄ alkyl groupand the other represents a halophenyl group.
 6. A compound as claimed inclaim 1 selected from the group consistingof6-(3-trifluoromethylphenoxy)-pyrazine-2-(N-(4-fluorophenyl))carboxamide;6-(3-trifluoromethylphenoxy)-pyrazine-2-(N-(2,4-difluorophenyl))carboxamide6-(3-trifluoromethylphenoxy)-pyrazine-2-(N-ethyl-N-phenyl)carboxamide;6-(3-trifluoromethylphenoxy)-pyrazine-2-(N-(2-fluorophenyl))carboxamide;and6-(1-methyl-3-trifluoromethylpyrazol-5-oxy)-pyrazine-2-(N-4fluorophenyl))carboxamide.7. A herbicidal composition comprising at least one compound of generalformula I, as claimed in claim 1, together with a carrier.
 8. A methodof combating undesired plant growth at a locus, comprising applicationto the locus with a compound of formula I, as claimed in claim 1.